Whether listening to an MP3 player while traveling, or to a high-fidelity stereo system at home, consumers are increasingly choosing earphones for their listening pleasure. Earphones are a pair of small loudspeakers that are designed to be held in place close to a user's ears. Earphones are also known as earspeakers and headphones. The alternate in-ear versions are known as earbuds or earpods. Earphones either have wires for connection to a signal source such as an audio amplifier, radio, CD player, portable media player, mobile phone, or electronic musical instrument, or have a wireless receiver, which is used to pick up signals without using a cable.
Most common types of speakers used in earphones have a housing that contains a moving coil driver. The moving coil driver consists of a stationary permanent magnet element affixed to the frame of the earphone which sets up a static magnetic field, and a diaphragm attached to a coil of wire (voice coil) that is immersed in the static magnetic field of the stationary magnet. The diaphragm is actuated by the attached voice coil when the varying current of an audio signal is passed through the coil. The alternating magnetic field produced by the current through the coil reacts against the static magnetic field, in turn causing the coil and attached diaphragm to move the air, thus producing sound.
An earphone system often includes a left earphone and a right earphone. Conventionally, an earphone system is designed such that the drivers of the left and right earphones are essentially identical so that they respond similarly to the same audio signal.